In the research and development of devices, circuits, and units that operate in the microwave band, measurement of phase differences between input signals to the devices, circuits, and units is indispensable. Conventionally, a VNA (Vector Network Analyzer) has fulfilled that role. A VNA is a device for measuring incident waves and reflected waves of a DUT (Device Under Test), or amplitude ratios and phase differences (S-parameters: scattering matrix elements) between incident waves and transmitted waves.
Conventionally a heterodyne type has been used as this sort of VNA. With the heterodyne type, measurement of an input signal is carried out by dropping the frequency of an input signal to an intermediate frequency using a local oscillator and a mixer.
However, with the heterodyne type high component accuracy is required, which often results in the device becoming expensive. Also, if the frequency of an input signal becomes high, there is a problem in that it becomes difficult to generate an intermediate frequency.
As means of solving these types of problems, a homodyne method has been proposed (refer to patent document 1 mentioned below). A six-port reflectometer is disclosed in this document. This is for calculating amplitude ratios and phase difference for two waves using system inherent hardware information obtained by calibration (calibration parameters) and a plurality of power measurement values (scalar quantities). According to this device and the measurement method using this device, phase differences for which high precision measurement would conventionally become difficult as the frequency becomes high can be obtained based on the measurement of scalar quantities of power which are basic measured quantities in electromagnetic wave measurement where measurement precision has almost no dependence on frequency. According to this technology, without being burdened by the demands of conventional high precision hardware, four power measurements and imperfections in hardware can be corrected with software (i.e. system parameters) known as calibration. A reflectometer is a unit for, for a single wave (signal), comparing an incident wave and reflected wave of that single wave.
Further, the present inventor has developed the technology of this publication to propose technology for composing a correlator (patent publications 2 to 7 below). A correlator (wave-correlator) is a unit that compares incident wave and reflected wave for two independent waves (of the same frequency), that is, measures complex amplitude ratios.